The chemical compound nitric oxide is a gas with chemical formula NO. It is an important signaling molecule in the body of mammals, including humans, and is one of the few gaseous signaling molecules known.
Nitric oxide is a key biological messenger, playing a role in a variety of biological processes in the human body. It is also known as endothelium-derived relaxing factor (“EDRF”) and is synthesized in vivo by a family of enzymes called nitric oxide synthases. It plays an important role in vasodilation, neurotransmission, and as part of the human immune response. For example, the endothelium of blood vessels uses nitric oxide to signal the surrounding smooth muscle to relax, thus dilating the artery and increasing blood flow. Nitric oxide is also used by plants.
Nitric oxide is also a toxic air pollutant produced by automobile engines and power plants.
The nitric oxide molecule is a free radical, which makes it very reactive and unstable. In air, it quickly reacts with oxygen to form nitrogen dioxide, signaled by the appearance of the reddish-brown color: 2 NO+O2→2 NO2.
One method of determining the concentration of nitric oxide is through electrochemistry. NO is oxidized by an electrode to induce a current change, which is proportional to concentration. However, there are some difficulties with this method. For example, a bare electrode is not selective and indiscriminately oxidizes multiple compounds. This results in interference and a poor NO signal, particularly in complex matrices (real media), such as biological media.
Some methods are known to increase the selectivity of an electrode. For example, selective membranes can be used with electrodes which exclude certain compounds from contact with the electrode. However, improvements are desirable.